Petroleum samples are complicated hydrocarbon mixtures containing paraffins, cyclic paraffins, multiring aromatics, and various heteroatomic hydrocarbons (most commonly O, S, and N). Produced petroleums contain molecules of a wide boiling point range from highly volatile C1-4 hydrocarbon gases to nonvolatile asphaltenes. Analysis of petroleum composition of various boiling ranges is valuable for improving the operation of many subsequent processes.
Detailed analysis of the composition of a petroleum sample is typically performed under controlled conditions in a laboratory setting. Due to the complexity of hydrocarbon or petroleum samples, analysis of composition usually involves a variety of sample preparations, such as performing an initial separation of a sample based on boiling point and/or chromatographic separation. Analysis of a whole crude sample is typically limited to bulk property characterization, such as determining a boiling point profile, an API gravity, or a sulfur content
In some instances, petroleum is derived from organic-rich sedimentary rocks. As these source rocks are heated, insoluble kerogen is converted to hydrocarbon and non-hydrocarbon products that are either expelled as petroleum or retained as soluble bitumen. The expelled petroleum migrates through other strata where it may leave surface stains or accumulate in porous reservoir rocks into accumulations.